Active capacitor multiplier in Miller-compensated circuits

Abstract

A technique is presented whereby the compensating capacitor of an internally compensated linear regulator, Miller-compensated two-stage amplifier, is effectively multiplied. Increasing the capacitance with a current-mode multiplier allows the circuit to occupy less silicon area and to more effectively drive capacitive loads. Reducing physical area requirements while producing the same or perhaps better performance is especially useful in complex systems where most, if not all, functions are integrated onto a single integrated circuit. Die area in such systems is a luxury. The increasing demand for mobile battery-operated devices is a driving force toward higher integration. The enhanced Miller-compensation technique developed in this paper helps enable higher integration while being readily applicable to any process technology, be it CMOS, bipolar, or BiCMOS. Furthermore, the technique applies, in general, to amplifier circuits in feedback configuration. Experimentally, the integrated linear regulator (fabricated in a 1-/spl mu/m BiCMOS process technology) proved to be stable for a wide variety of loading conditions: load currents of up to 200 mA, equivalent series resistance of up to 3 /spl Omega/, and load capacitors ranging from 1.5 nF to 20 /spl mu/E The total quiescent current flowing through the regulator was less than 30 /spl mu/A during zero load-current conditions.